The present invention relates to aspiration systems used in phacoemulsification procedures, and more particularly, to aspirations systems employing small bore elements to improve operation.
Typical surgical instruments suitable for phacoemulsification procedures on cataractous lenses include an ultrasonically driven phacoemulsification hand piece with a cutting needle and an irrigation sleeve, and a control console. The hand piece is attached to the control console by an electric cable and flexible tubing. The flexible tubing supplies irrigation fluid to the surgical site and carries aspiration fluid from the surgical site to a waste or discard reservoir.
During a phacoemulsification procedure, the tip of the cutting needle and the end of the irrigation sleeve are inserted into the anterior segment of the eye through a small incision in the eye's outer tissue. The surgeon brings the tip of the cutting needle into contact with the lens of the eye, so that the vibrating tip fragments the lens. The resulting fragments are aspirated out of the eye through the interior bore of the cutting needle, along with irrigation fluid provided to the eye during the procedure.
Throughout the procedure, irrigating fluid is infused into the eye, passing between the irrigation sleeve and the cutting needle and exiting into the eye at the tip of the irrigation sleeve and/or from one or more ports or openings formed into the irrigation sleeve near its end. This irrigating fluid prevents the collapse of the eye during the removal of the emulsified lens, protects the eye tissue from the heat generated by the vibrating of the ultrasonic cutting needle, and suspends the fragments of the emulsified lens for aspiration from the eye.
During the surgical procedure, the console controls irrigation flow rates and aspiration flow rates to maintain a proper intra-ocular chamber balance in an effort to maintain a relatively consistent fluid pressure at the surgical site in the eye.
Aspiration flow rates of fluid from the eye are typically regulated by an aspiration pump that creates a vacuum in the aspiration line. The aspiration flow and/or vacuum are set to achieve the desired working effect for the lens removal. While a consistent fluid pressure in the eye is desirable during the phacoemulsification procedure, common occurrences or complications create fluctuations or abrupt changes in fluid flow and pressure at the eye. One known cause for these is occlusions or flow obstructions that block the needle tip. This common, and sometimes desirable occurrence, results in a sharp increase in vacuum in the aspirating line. When the occlusion is removed, the resulting high demand for fluid from the eye to relieve the vacuum can cause a sudden shallowing of the anterior chamber, as the aspiration flow momentarily sharply increases over the irrigation flow.
The degree of shallowing in the eye is a function of vacuum level within the aspiration path when the occlusion breaks, as well as resistive and compliance characteristics of the fluid path. Increased resistance in the aspiration path reduces the flow rate associated with occlusion break and thereby lessens the pressure drop from the irrigating source to the eye and the resulting shallowing of the anterior chamber.
The problem of occlusion surge has been addressed in the past in a number of ways. One method includes adding a reduced cross-sectional orifice to create a barrier reducing flow. While such a reduced area reduces the effects of occlusion surge, reduction of aspiration path cross-section can also increase the potential for clogging during the procedure. Other methods have been used or proposed that involve torturous paths, with corners, angles, and fluid restrictors that are also subject to clogging. Some prior solutions involve a resistive element at or near the pump. However, the effectiveness of these solutions is limited due to the relatively large tubing compliance between the resistive element and the eye. Another attempted solution has been the use of increased lengths of flexible aspiration tubing in an attempt to increase overall tubing resistance. This solution of adding flexible tubing length has the undesirable effect of adding additional compliance to the aspiration path. The additional compliance increases the demand for fluid from the eye during occlusion break, sometimes entirely offsetting the benefits obtained by the longer tubing length.
Methods with small bore aspiration lines, such as lines with a diameter of 0.050 inches or less, have generally been avoided because small bore lines may become easily clogged, potentially creating inconsistent flow rates, resulting in high levels of occlusion surge, and possibly resulting in undesirable levels of trauma during the surgical procedure. In addition, methods with small bore aspiration lines have generally been avoided because, as a result of the small bore with increased wall resistance, pumping that achieves a desirable flow rate can be difficult.